A transmission system using a plurality of sub carriers of an OFDM (orthogonal frequency division multiplexing) system or the like is utilized not only in wireless communication but also in wired communication. Although a transmission system using a plurality of sub carriers achieves a significant advantage that high quality communication can be executed even in a severe transmission path, depending on a quality of a transmission path, there is a case in which a radiation power is increased to effect an influence on outside.
According to communication of the OFDM system, a transmission power is controlled and a modulating system is selected for respective carriers on a transmission side based on a result of measuring power on a receiving side (refer to JP-A-2003-152671, JP-A-2003-218831) As shown by JP-A-2003-152671, in multi carrier wireless communication, it is ordinarily carried out to inform a received power value of a sub carrier detected on the receiving side to the transmission side and control a transmission power of the sub carrier on the transmission side receiving the received power value. Further, JP-A-2003-218831 describes a technology of selecting a sub carrier used in accordance with a situation of a communication error detected on the receiving side in the wired transmission of the OFDM system.
However, in either of the technologies shown in JP-A-2003-152671, JP-A-2003-218831, a transmission signal is controlled by utilizing a result of processing the receiving signal on the receiving side and the system is not simply constructed. Further, the influence of the radiation power cannot necessarily be reduced.